Landsat imagery applications to identify vegetation recovery from acidification in mountain catchments 121Křeček, J. and Krčmář, V. Hungarian Geographical Bulletin 64 (2015) (2) 121–126. Landsat imagery applications to identify vegetation recovery from acidifi cation in mountain catchments Josef KŘEČEK and Vlastislav KRČMÁŘ1 Abstract In the 1980s, headwater catchments of the Jizera Mountains (Czech Republic) were degradated by the extreme acid atmospheric deposition, die-back of spruce plantations (Picea abies), and commercial forestry practices. The aim of this study is to evaluate long-term changes in the vegetation canopy within two catchments of drink- ing water reservoirs Josefův Důl and Souš, using the Landsat imagery archive, 1984–2010. The ground-based evidence of canopy characteristics was carried out in the Jizerka experimental basin on plots 30 x 30 m. The supervised classifi cation of multi-band raster images was found eff ective to describe long-term changes in the canopy of investigated catchments. The NDVI index can well identify succession of herbaceous communities aft er the clear-cut. However, NDVI values were not sensitive to detect changes in the canopy structure of dense spruce stands where the horizontal canopy density exceeds 30 percent. Keywords: forested mountain watershed, canopy density, acid atmospheric deposition, Landsat imagery, normalised diff erence vegetation index Introduction Pike, R.G. et al. (2010) referred to a highly signifi cant role of forest canopy in the run- off genesis, particularly in a mountain catch- ment. Methods of remote sensing and image interpretation focused on indicating the for- est canopy have been used in many projects worldwide (Lillesand, T. and Kiefer, R.W. 1987; Wolter, P.T. et al. 1995; Burroughs, P.A. and McDonnell, R.A. 1998). Since 1972 Landsat satellites have continuously and consistently archived images of Earth, and the Landsat Programme provides the long- est continuous space-based record of Earth’s land with applications in many types of envi- ronmental studies (NASA 2014). Applications of the Landsat imagery are now supported by NASA (2014) and the Global Land Cover Facility (GLCF, 2014), free to download. The Jizera Mountains (Czech Republic, 50°40’–50°52’N, 15°08’–15°24’E, humid tem- perate zone) is part of the so-called "Black Triangle", the epicentre of acid atmospheric deposition in Europe (Figure 1). The region includes a 200 km2 forest pla- teau above 800 m elevation with dominant spruce plantations (Picea abies), important particularly for the national water resource recharge. In the 1980s, this area was degrad- ed by acidifi cation, defoliation and die-back of spruce stands, and the commercial forest harvest (Křeček, J. and Hořická, Z. 2010). The association Junco eff usi-Calamagrostietum villosae became a dominant community there, reported by Křeček, J. et al. (2010). Although the reforestation followed immediately aft er clear-cut, there was relatively slow progress in the forest stand development because of the competition of invasive grasses and the 1 Department of Hydrology, Czech Technical University in Prague, Thákurova 7, CZ-166 29 Prague 6. E-mail: josef.krecek@fsv.cvut.cz DOI: 10.15201/hungeobull.64.2.3 Hungarian Geographical Bulletin 64 2015 (2) 121–126. Křeček, J. and Krčmář, V. Hungarian Geographical Bulletin 64 (2015) (2) 121–126.122 Fig. 1. Focused headwater catchments in the Jizera Mountains high level of acidifi cation. The aim of this study is to evaluate long-term changes (1984– 2010) in the vegetation canopy of three head- water catchments in the Jizera Mountains by analysing the Landsat imagery data, sup- ported by the standard ground survey. Material and methods Three headwater catchments with dominant spruce plantations were analysed in this study: the experimental basin Jizerka (J), and two basins of drinking water reservoirs Josefův Důl (JD) and Souš (S). Basic morpho- logical characteristics of the focused catch- ments are given in Table 1. From the archive of Landsat imagery, clear-sky images of summer seasons (June– August) were taken into account. This timing corresponds to recommendations of Chen, J.M. and Cihlar, J. (1996) to avoid an under- estimating the herbaceous layer. The normal- ised diff erence vegetation index (NDVI) was evaluated, and images classifi ed respecting diff erent types of the vegetation cover. The NDVI index was calculated for the spectral refl ectance registered in the visible (red) and near-infrared bands, equation (1) according to Weier, J. and Herring, D. (2000). NDVI = (NIR–VIS)/(NIR+VIS), (1) where NIR = near infrared radiation (0.7–1.1 μm), VIS = visible radiation (0.4–0.7 μm). Also the supervised classifi cation of multi- band raster images (Landsat 4,5) was em- ployed. For collected samples (representing distinct sample areas of diff erent canopy) the images were classifi ed by the image ana- lyst (Nagi, R. 2011). The estimated canopy classes were used to extrapolate outcomes of the detailed environmental monitoring at the experimental basin (J) to larger catchments of water reservoirs (JD and S). In the experimental basin (J), ground- based evidence (squares of 30 x 30 m, cor- responding to the Landsat image resolution) of canopy characteristics was carried out an- nually respecting seasonal patt erns of the herbaceous layer (Křeček, J. et al. 2010). The respected canopy classes taking into account by this study included: clear-cut, Table 1. Characteristics of the basins Jizerka (J), Josefův Důl (JD) and Souš (S) Basin Area (A), km2 Mean elevation (E), m Mean slope (S), % Length (L), km Shape index A/L2 (-) J JD S 1.03 19.64 13.78 927 834 865 12.00 11.90 14.00 1.14 5.49 5.06 0.79 0.65 0.54 123Křeček, J. and Krčmář, V. Hungarian Geographical Bulletin 64 (2015) (2) 121–126. herbaceous vegetation (with Calamagrostis sp. dominant), reforested areas (mostly by spruce again) respecting the crown closure limit of 0.3, and mature spruce stands. This adopted scheme roughly corresponds with the defi ni- tion of “forest” used by the United Nations Framework Convention on Climate Change (crown closure > 0.1–0.3 and height >2–5 m at maturity) (Sasaki, N. and Putz, F.E. 2009). Results and discussion The distribution of representative canopy clusters in investigated catchments (J, JD and S) have been shown in Figure 2, and the corresponding percentage of class-evidence within watershed areas have been given in Figure 3 (for time horizons of 1984, 1992, 2002 and 2010). The analysed changes in vegetation cover show similar trend in all the investigated catchments: high clear-cut evidence (from 30 to 60%) in the 1980s, dominant herba- ceous communities in the 1980s and 1990s (included the reforested sites with low crown closure), and intensive recovery of spruce stands in the 2000s (some 20% increase in stands with crown closure over 0.3, during the last ten years). The NDVI index plott ed against crown closure (Figure 4) shows a negative re- lationship between NDVI values and horizontal density of spruce canopy. Estimated NDVI val- ues (0.65–0.76) cor- respond to the NDVI range of 0.6–0.8, in- troduced for temper- ate forests by Weier, J. and Herring, D. (2000). However, in our study, the grass community shows h igher va lues of NDVI (0 .72–0.76) against spruce stands (0.65–0.72). Similar results were reported also by Gamon, J.A. et al. (1995) finding relatively insensitive NDVI values to iden- Fig. 2. Changed canopy struc- ture at J, JD and S basins Křeček, J. and Krčmář, V. Hungarian Geographical Bulletin 64 (2015) (2) 121–126.124 Fig. 3. Changed clear-cut and reforestation in J, JD and S basins tify changes in the canopy structure of dense shrubs and trees (by leaf area index LAI > 2). The impact of commercial forest clear-cut on runoff genesis was studied in the experi- mental basin J since 1982. In 1992, aft er the harvest of spruce plantations, the drainage network extended from 1.5 to 6.6 km/km2 (Figure 5). The extended drainage in the basin is a result of skidding the harvested timber by wheeled tractors. Twenty years aft er, with a spontaneous succession of grasses, and forest recovery, the drainage density was reduced back again to 1.8 km/km2. The development of drainage network de- scribed in Figure 5 could be interpreted in an extrapolation of drainage network by the clear-cut class occurrence in watersheds JD and S (see Figure 2). Conclusion The supervised classifi cation of multi-band raster images (Landsat 4.5) was found very useful to describe long-term changes in the canopy of mountain watersheds aff ected by the acid atmospheric deposition. The esti- mated canopy classes addressed: clear-cut of spruce plantations, dominant herbaceous layer, reforested areas with crown closure be- low or over 30%, and mature spruce stands (see Figure 3). The identifi cation of clear-cut within a catchment could be used to ex- trapolate the estimates of drainage network changes, based on the detailed study in the experimental basin (see Figure 5). The application of NDVI index in this study was limited by the crown closure of spruce (approximately by 0.3) (see Figure 4). The grass Fig. 4. NDVI index and the hori- zontal canopy density (estimated by the ground survey) 125Křeček, J. and Krčmář, V. Hungarian Geographical Bulletin 64 (2015) (2) 121–126. Fig. 5. The risk of concentrated fl ow from the digital elevation model (on top), and drainage network aft er the clear-cut of spruce plantations, J basin, 1992 (at the bott om) community showed higher values of NDVI (0.72–0.76) against spruce stands (0.65–0.72). Therefore, NDVI values are relatively insensi- tive to identify changes in the canopy structure of dense spruce stands (by horizontal canopy density over 30%). However, NDVI index can well identify succession of herbaceous layers aft er the clear-cut. It seems to be important, particularly, in indicating the protection of soil surface and recovery of erosion rills. Acknowledgements: This research was supported by the Earthwatch Institute (Oxford, UK, Mountain Waters of Bohemia), and by the Czech Technical University in Prague (SGS 14/128/OHK1/2T/11). REFERENCES Burroughs, P.A. and McDonnell, R.A. 1998. Principles of Geographical Information Systems. Oxford, Oxford University Press, 327 p. Chen, J.M. and Cihlar, J. 1996. Retrieving leaf area in- dex of boreal conifer forests using Landsat TM im- ages. Remote Sensing of Environment 56. 153–162. Gamon, J.A., Field, Ch.B., Goulden, M.L., Griffin, K.L., Hartley, A.E., Geeske J., Penuelas J. and Valentini, R. 1995. Relationships between NDVI, canopy structure, and photosynthesis in three Californian vegetation types. Ecological Applications 5. 28–41. GLFC, 2014. Landsat imagery. Global Environmental Facility, htt p://glcf.umd.edu, accessed on the 24th October 2014. Křeček, J. and Krčmář, V. Hungarian Geographical Bulletin 64 (2015) (2) 121–126.126 Křeček, J. and Hořická, Z. 2010. 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